DigiTally: Piloting Offline Payments for Phones


Khaled Baqer and Ross Anderson, Computer Laboratory, University of Cambridge; Lorna Mutegi, Strathmore University; Jeunese Adrienne Payne, Independent Consultant; Joseph Sevilla, Strathmore University


Mobile payments support a range of services in many less developed countries including everyday payments, migrant remittances, credit, tax collection, and welfare benefits. These services depend entirely on the mobile phone network as their carrier, so they stop where the network does. This leaves millions of the very poorest people stranded — people living in remote areas where there is little to no network service. It also leaves urban users at the mercy of network congestion.

We developed a prototype system, DigiTally, which lets users make offline payments by copying short strings of digits from one mobile handset to another. Offline payments are already used for electricity (both in prepayment meters and pay-as-you-go solar); can we extend them into a general-purpose payment system, to increase service resilience in the face of network congestion or outage, and provide service to currently excluded areas?

We report the results of a preliminary study with an early prototype of DigiTally, tested on participants from a university in Nairobi (Kenya). The code-sharing process presented a possible usability challenge. To explore this and other aspects of an early prototype, DigiTally was introduced to Kenyan participants in order to resolve any major issues before a later field trial.

We discuss the lessons learned from our field visits and initial evaluation; we hope that this contribution is helpful for researchers and policy makers interested in mobile payments and financial inclusion. We also present our findings and observations. We found that, although offline payments involve copying codes in both directions between the payer's phone and the payee's, the extra workload was acceptable to most users.

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@inproceedings {205128,
author = {Khaled Baqer and Ross Anderson and Lorna Mutegi and Jeunese Adrienne Payne and Joseph Sevilla},
title = {{DigiTally}: Piloting Offline Payments for Phones},
booktitle = {Thirteenth Symposium on Usable Privacy and Security (SOUPS 2017)},
year = {2017},
isbn = {978-1-931971-39-3},
address = {Santa Clara, CA},
pages = {131--143},
url = {},
publisher = {USENIX Association},
month = jul

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